DESCRIPTION: (Applicant's Description) The Cooperative Breast Cancer Tissue Resource (CBCTR) represents a collaboration between four institutions that possess archives with large numbers of formalin-fixed breast cancer specimens. These four sites, under Cooperative Agreements with the NCI, have created the CBCTR as a tissue resource for investigators of breast cancer. The CBCTR was originally conceived to provide large numbers of specimens particularly for definitive studies of prognostic markers. The CBCTR has enrolled nearly 9,000 archival breast cancer specimens together with clinical and follow-up information about each case. The material exists as a "virtual bank" with the actual specimens remaining at the individual sites but a Central Database tracking each specimen. The database is mounted on the World Wide Web and may be searched by investigators seeking to ascertain the number and type of material available from this resource. Investigators may then apply to the CBCTR for tissue specimens. Applications are reviewed by a panel of experts, the Research Evaluation Panel, for scientific merit and by the CBCTR Coordinating Committee of Principal Investigator's for feasibility, prior to providing the requested specimens. Kaiser Permanente, Northwest Division has provided over 2,500 specimens to the CBCTR and is reapplying for funding to continue its efforts in this project. This highly integrated and stable medical care system represents an ideal setting for such a project. It has diagnosed a large number of breast cancers since 1970, has archived all such specimens and has complete clinical and follow-up information in its files on all patients. Finally, this organization is committed to research in the public domain and seeks to share its resources with others in the pursuit of breast cancer research.